Reflected light detecting device and method with surface reflected light components collectively be extracted/removed when detecting reflected light arising in casting light onto target-object range having non-planar surface. The device includes: a first illuminating device causing first-measurement light in predetermined polarization direction to enter target-object first region from first direction; polarization optical system position part of first-surface reflected light enters the polarization optical system, the first-surface reflected light being the first-measurement in the first region surface; a second illuminating device causing second-measurement light in the same first-measurement light polarization direction to enter second region from second direction, the second region being on the target-object surface, different from the first region; adjusting direction of the second-measurement light optical axis so part of second-surface reflected light enters the polarization optical system, the second-surface reflected light being the second-measurement in second region surface; and detecting light having passed through the polarization optical system.